feat[lang]!: change the signature of block.prevrandao (#3879)

`block.prevrandao` is an opcode alias for `difficulty`. however, it
returns a bytes object at the evm level (cf. for instance py-evm returns
the value of `block.mixhash`). this commit changes the signature of
`block.prevrandao` to be more consistent with the VM semantics.

also update PR title regex per conventional commit specification - add
optional `!` which indicates a breaking change

.github/workflows/pull-request.yaml

@@ -49,6 +49,8 @@ jobs:
           subjectPatternError: |
             Starts with uppercase letter: '{subject}'
             (Full PR title: '{title}')
-          headerPattern: '^(\w*)(?:\[([\w$.\-*/ ]*)\])?: (.*)$'
+          # type[scope]<optional !>: subject
+          # use [] instead of () for aesthetics
+          headerPattern: '^(\w*)(?:\[([\w$.\-*/ ]*)\])?!?: (.*)$'
           validateSingleCommit: true
           validateSingleCommitMatchesPrTitle: true

docs/constants-and-vars.rst

@@ -16,7 +16,7 @@ Name                 Type             Value
 ==================== ================ =========================================================
 ``block.coinbase``   ``address``      Current block miner's address
 ``block.difficulty`` ``uint256``      Current block difficulty
-``block.prevrandao`` ``uint256``      Current randomness beacon provided by the beacon chain
+``block.prevrandao`` ``bytes32``      Current randomness beacon provided by the beacon chain
 ``block.number``     ``uint256``      Current block number
 ``block.prevhash``   ``bytes32``      Equivalent to ``blockhash(block.number - 1)``
 ``block.timestamp``  ``uint256``      Current block epoch timestamp
@@ -31,7 +31,7 @@ Name                 Type             Value
 
 .. note::
 
-    ``block.prevrandao`` is an alias for ``block.difficulty``. Since ``block.difficulty`` is considered deprecated according to `EIP-4399 <https://eips.ethereum.org/EIPS/eip-4399>`_ after "The Merge" (Paris hard fork), we recommend using ``block.prevrandao``.
+    ``block.prevrandao`` is an alias for the ``block.difficulty`` opcode. Since ``block.difficulty`` is considered deprecated according to `EIP-4399 <https://eips.ethereum.org/EIPS/eip-4399>`_ after "The Merge" (Paris hard fork), we recommend using ``block.prevrandao``.
 
 .. note::
 

tests/functional/syntax/test_block.py

@@ -138,7 +138,7 @@ def foo():
     """
 @external
 def foo():
-    x: uint256 = block.prevrandao + 185
+    x: bytes32 = block.prevrandao
     if tx.origin == self:
         y: Bytes[35] = concat(block.prevhash, b"dog")
     """,

vyper/codegen/expr.py

@@ -270,7 +270,7 @@ def parse_Attribute(self):
                     warning = "tried to use block.prevrandao in pre-Paris "
                     warning += "environment! Suggest using block.difficulty instead."
                     vyper_warn(warning, self.expr)
-                return IRnode.from_list(["prevrandao"], typ=UINT256_T)
+                return IRnode.from_list(["prevrandao"], typ=BYTES32_T)
             elif key == "block.difficulty":
                 if version_check(begin="paris"):
                     warning = "tried to use block.difficulty in post-Paris "

vyper/semantics/environment.py

@@ -19,7 +19,7 @@ class _Block(_EnvType):
     _type_members = {
         "coinbase": AddressT(),
         "difficulty": UINT256_T,
-        "prevrandao": UINT256_T,
+        "prevrandao": BYTES32_T,
         "number": UINT256_T,
         "gaslimit": UINT256_T,
         "basefee": UINT256_T,